The present invention relates to a recoverable, especially to a heat-recoverable, article and a method for protecting or shielding a junction or discontinuity in cables or conduits for example coaxial cables and other cables having a conductive outer shield from external radio frequency interference.
Heat recoverability is characterized by the ability to undergo a permanent change in dimensions with the application of heat. In general, the property of heat recoverability can be imparted to a material having a plastic or elastic memory by deforming the material at an elevated temperature to a size different from its normal size and then cooling while maintaining the material in the deformed size.
The prior art methods of shielding cables from external radio frequency interference have been plagued by the problem of leakage. The problem is particularly acute at a junction between two or more such cables where it is important that the continuity of the outer conductive shield be maintaned in both longitudinal and circumferential directions in order to provide adequate screening against stray radiation.
The use of heat-recoverable tubing in connection with the shielding and protecting of cable junctions and the like is known. Also, the use of a heat-shrinkable tubing "sandwiched" with conductive braid is known as described in U.S. Pat. No. 3,253,619, the disclosure of which is incorporated herein by reference. Although braided shields have been used to protect coaxial cables from radio frequency interference I have perceived that the utility of these shields could be greatly enhanced if the shield could be formed to protect the cable from high frequency radiation which is capable of penetrating the interstices between the strands of a braided shield and shaped so that it is capable of deforming uniformly when the tubing with which it is sandwiched is caused to be recovered.
It is thus an object of the present invention to provide a recoverable, especially a heat-recoverable article for effectively protecting or shielding a junction or discontinuity in conduits or cables from radio frequency interference, water, gas, solvents etc.
This and other objects are accomplished by shielding or protecting a junction or discontinuity in conduit or cable with an article comprised of a member of heat-recoverable material having a corrugated sheath disposed therein.
In my co-pending U.S. Ser. No. 504,375 (British patent application No. 42483/73), the disclosure of which is incorporated by reference herein. I provide an assembly for such purposes which comprises a hollow shrinkable component and a longitudinally corrugated sheath of external diameter such that is may be inserted into the shrinkable component (i.e., while the latter is in an expanded state) and of internal diameter such that it may be positioned over the substrate to be protected. Advantageously the hollow shrinkable component is a sleeve, and is heat-shrinkable, and the sheath is disposed internally in and coaxially with the sleeve.
The corrugations are preferably substantially parallel to the axis of the sheath but may be inclined thereto, e.g., up to about 45.degree..
The present invention provides an assembly which comprises a hollow shrinkable component and a corrugated sheath, of external cross-section such that it may be inserted into the shrinkable component, the sheath having longitudinal corrugations extending over substantially the whole of its length and transverse corrugations extending over a part, preferably the central region, only of its length.
The longitudinal corrugations are preferably parallel to the axis of the sheath and, where the shrinkable component is a sleeve, the sheath and sleeve preferably being coaxial, to the axis of the shrinkable component, but they may be inclined at up to about 45.degree. thereto. The transverse corrugations are preferably perpendicular to the axis of the sheath, and preferably perpendicular to the longitudinal corrugations, but they may be inclined to the axis at an angle of at least 45.degree., preferably being at right angles to the longitudinal corrugations.
The longitudinal corrugations preferably extend from a first end to a second end of the sheath and regions containing only such corrugations are collapsible inwardly upon the imposition of the radially inward force of recovery, especially heat-recovery, to reduce the mean cross-section, e.g. the diameter, of the sheath.
A region which also contains transverse corrugations is by contrast sufficiently rigid to withstand the inward force of recovery of the shrinkable component so that recovery in that region or those regions is inhibited.
By appropriate choice of region(s) having both types of corrugations and region(s) having longitudinal corrugations, the shrinkage of the shrinkable component may be controlled as desired for any particular end-use.